//:C15:Instrument3.cpp
// Late binding with the virtual keyword
#include <iostream>
using namespace std;

enum note { middleC, Csharp, Cflat };    // Etc.

class Instrument
{
    public:
        virtual void play(note) const
        {
            cout << "Instrument::play" << endl;
        }
};

// Wind objects are Instruments
// because they have the same interface:
class Wind : public Instrument
{
    public:
        // Override interface function:
        void play(note) const
        {
            cout << "Wind::play" << endl;
        }
};

void tune(Instrument &i)
{
    // ...
    i.play(middleC);
}

int main(void)
{
    Wind flute;
    tune(flute);    // Upcasting
}